1. Field of the Invention
The present invention relates to a method of multimedia broadcast multicast service (MBMS) content aware scheduling and receiving in a wireless communication system and related communication device, and more particularly, to a method for scheduling MBMS services of different resolution levels and for receiving an MBMS service according to requirements on the resolution level when performing the MBMS service and related communication device.
2. Description of the Prior Art
A long-term evolution (LTE) system, initiated by the third generation partnership project (3GPP), is now being regarded as a new radio interface and radio network architecture that provides a high data rate, low latency, packet optimization, and improved system capacity and coverage. In the LTE system, an evolved universal terrestrial radio access network (E-UTRAN) includes a plurality of evolved Node-Bs (eNBs) and communicates with a plurality of mobile stations, also referred as user equipments (UEs). The LTE radio protocol stack includes the Layer 3, also known as the Radio Resource Control (RRC) layer, the Layer 2, consisting of three sub-layers that are the Packet Data Convergence Protocol (PDCP) layer, the Radio Link Control (RLC) layer, and the Medium Access Control (MAC) layer, and the Layer 1, also known as the Physical (PHY) layer.
Recently, the 3GPP is involved in the further advancements for E-UTRA and proposes an LTE-Advanced system as an enhancement of the LTE system. Carrier aggregation, where two or more component carriers are aggregated, is introduced into the LTE-Advanced system in order to support wider transmission bandwidths, e.g. up to 100 MHz and for spectrum aggregation. A UE of the LTE-Advanced system can simultaneously receive and/or transmit on multiple component carriers. Carrier aggregation allows a UE to aggregate a different number of component carriers of possibly different bandwidths in uplink and downlink.
Evolved multimedia broadcast multicast service (E-MBMS) has been introduced in the LTE specification to broadcast or multicast TV, films, information such as free overnight transmission of newspaper in a digital form. Two important scenarios have identified for the E-MBMS: one is single-cell broadcast, and the other is E-MBMS over a single frequency network (MBSFN). The MBSFN is a simulcast transmission technique that realizes transmission of identical waveforms at the same time from multiple cells covering a geographic area called an MBSFN area. A UE therefore observes multiple versions of the signal with different delays due to the multi-cell transmission. Since the MBSFN transmissions from the multiple cells are closely time-synchronized, the MBSFN transmission arrived at the UE is regarded as a transmission from a single cell and the UE may treat the MBSFN transmission in the same way as multi-path components of a single cell transmission without additional complexity. The MBSFN transmission takes place on dedicated subframes referred to as MBSFN subframes, which may also be used for non-MBMS data transmission when the MBSFN subframes are not allocated for MBMS data.
Please refer to FIG. 1, which is a diagram of E-MBMS architecture according to the prior art. A broadcast/multicast service center (BMSC) receives MBMS data generated from an MBMS content provider. An MBMS gateway is present between the BMSC and eNBs for delivering MBMS data to each eNB providing the MBMS service. A multicast coordination entity (MCE) is present between a mobility management entity (MME) and eNBs for allocating radio resources used by all eNBs in the MBSFN area for multi-cell MBMS transmission. The MCE may be a part of an eNB or another network element than E-UTRAN. To realize E-MBMS, the PHY layer of the LTE system offers information transfer services between a physical multicast channel (PMCH) and a downlink transport channel called multicast channel (MCH). The MCH is required to be broadcasted in the entire coverage area of each cell in the MBSFN area. Scheduling of each MCH is done by the MCE. The MAC layer of the LTE system offers data transfer services between the MCH and logical channels including a multicast traffic channel (MTCH) and a multicast control channel (MCCH), which are point-to-multipoint channels for transmitting traffic data and control information. Within MBSFN subframes, the transmission of a specific MCH carrying MTCH occupies a pattern of subframes which are not necessarily adjacent in time, called MCH subframe allocation pattern (MSAP). The MSAP for every MCH is signalled on the MCCH. The MSAP occasion comprises a set of subframes defined by the MSAP during a certain period.
A UE determines what subframes are used by each MTCH according to a dynamic scheduling information (DSI), which is generated by the eNB and allocated in the first subframe of the MSAP occasion, for indicating subframes used by each MTCH in the MSAP occasion. The DSI can be carried in an MAC control element or in a separate logical channel, such as a multicast scheduling channel (MSCH). Up to now, in 3GPP meetings, information that shall be included in the DSI is still under discussion.
The latest trend of mobile communication devices shows an increasing demand of smartphones, netbooks, or mobile internet devices, which are more diversified than ordinary mobile phones and enable advanced computing ability to implement a video compression standard such as H.264 or MPEG-4 commonly used for a video streaming service. That video compression standard is also foreseen to be used by E-MBMS. In the field of video compression, a video frame is compressed using different algorithms that are also called frame types, such as intra-frame (I-frame) or predicted frame (P-frame). An I-frame is the least compressible but does not require other video frames to decode, such as a conventional static image file. A P-frame, also known as a delta-frame, holds only the changes in the image from the previous frame and can use data from previous frames to decompress, which is more compressible than an I-frame. I-frames can be regarded as low-resolution data to present the least necessary information of a video, and P-frames can be regarded as high-resolution data to bring more detailed information. For an MBMS service as a video streaming service, an MBMS service of a high resolution level may include I-frames and P-frames to present the detail and an MBMS service of a low resolution level may include I-frames only. What resolution level an MBMS service is in depends on the number of resolutions the MBMS data (such as video frames) of the MBMS service have.
Note that, mobile communication devices having different screen sizes may have different requirements with respect to the resolution level when performing MBMS services. For example, a laptop computer is supposed to use a resolution level higher than that a smartphone uses for MBMS services. In addition, for a mobile communication device, a user may have different requirements on the same MBMS service at different time. For example, after the user shrinks the window size of a streaming video, the required resolution level of the video can be lowered. The user may use a picture-in-picture function when watching two or more videos in which one on the full screen requires a higher resolution level and the other in an inset window only requires a lower resolution level. In addition, the user may switch an active window of an MBMS service to another application window and puts the MBMS service window to the background, then only minimum resolution level is required or the mobile communication device stops receiving MBMS data until the user switches back to the MBMS service window.
However, the eNB has no way to know the screen size of each UE or how the user watches the MBMS service currently, and can only schedule an MBMS service including data having all levels of resolution to all UEs receiving the MBMS service. Each UE receives and decodes the same MBMS data, and thereby parts of MBMS data of required resolutions are recognized. If a UE requires only low-resolution MBMS data to be displayed, high-resolution MBMS data already decoded are discarded or unused and power consumption for receiving and processing these high-resolution MBMS data is wasted, which is a critical issue for UEs using batteries as a power source.